Patients who suffer from disabilities which are specific to reading are generally less sensitive when measured for pattern contrast sensitivity at low spacial frequencies and they generally have greater difficulty in detecting visual flicker than normal readers. In addition, they exhibit slower rates of visual search and have greater difficulty than normal readers in perceptual grouping tasks. Also they require longer separation times before they can correctly report which of two temporally asynchronous patterns appeared first, and they make larger errors when asked to specify the spatial location of a flashed pattern. However, there is no obvious visual problem to account for this disability in that if the patient's eyes were tested by an optometrist they would be found to be essentially normal.
It is known from a published paper (Williams M. C., Brannan J. R. and Latrigue E. K. "Visual Search in Good and Poor Readers" Clinical Vision Sciences 1 Pages 367-371 (1987) that improved visual search results can be achieved if a certain degree of blur is provided by the use of especially prepared diffusing filters which have the effect of removing some of the medium to high spatial frequency information perceived by the viewer.
It is also known to use tinted glasses termed "Irlen Lenses" for the treatment of reading problems, however, there is no rigorous or systematic way in which the colour of the tint which produces either an improved, or optimum, result can be determined. Rather, various subjective judgements as to the efficacy of various tints are made on the basis of the patient's reported perceptions.
As a consequence of the subjective nature of the Irlen Lenses procedures, the procedures are extremely time consuming and do not provide a sound basis for prescription. It is also extremely difficult to determine whether or not the patient is improving as a result of the particular tinted lenses selected.
The present inventors have discovered arrangements which are based upon the sustained and transient theory of visual perception and which enable a predictive basis for improved results to be achieved, thereby enabling not only greater overall improvement, but also a substantial reduction in the time required for testing prior to the prescription of corrective apparatus, and indeed the ability to be able to prescribe at all.